The present invention relates to a method for forming a patterned resist layer on a metallic substrate surface or, more particularly, to a method for forming a patterned resist layer on the surface of a substrate of which at least the surface layer is made from a metal such as tantalum with greatly improved adhesion between the resist layer and the metallic surface.
It is a well established technology in the manufacture of various kinds of semiconductor devices such as ICs and LSIs and liquid crystal display units that the surface of a metallic substrate of aluminum, tantalum, molybdenum, chromium and the like is finely worked by the etching method in which a thin layer of a photosensitive resin composition is formed on the substrate surface as a resist layer which is patterned by the photolithographic process by first exposing the resist layer pattern-wise to actinic rays such as ultraviolet light through a patterned photomask to form a latent image which is developed with a developer solution to give a patterned resist layer to be used as a resist in the etching of the metallic substrate surface with an etching solution. Various types of photosensitive resin compositions are known in the prior art to be suitable for the above mentioned purpose, of which those quite satisfactory include positive-working photosensitive resin compositions comprising an alkali-soluble novolac resin as a film-forming ingredient and a quinone diazide group-containing organic compound or, in particular, a quinone diazide group-containing benzophenone compound as a photosensitive ingredient (see, for example, U.S. Pat. No. 4,377,631 and Japanese Patent Kokai 62-35349, 1-142548 and 1-179147).
In the photolithographic etching process of a metallic substrate surface in the manufacture of semiconductor devices and liquid crystal display units, one of the requirements for the photoresist composition is that the adhesion between the patterned resist layer and the metallic substrate surface is very firm while none of the photosensitive resin compositions of the above mentioned type is quite satisfactory in this regard, especially, when the substrate has a surface of tantalum although these resist compositions can exhibit good adhesion to the surface of a substrate such as a semiconductor silicon wafer. Accordingly, it is eagerly desired to develop a method for forming a patterned resist layer capable of exhibiting excellent adhesion to the substrate surface even when the substrate has a metallic surface.
Various proposals and attempts have been made in order to improve adhesion between a photoresist layer and a substrate surface. For example, Japanese Patent Kokai 62-180357 teaches admixture of a photopolymerizable monomeric composition with a benzimidazole compound as an adhesion improver. Although this method is effective when the substrate is a silicon wafer, no particular improvement can be obtained in the adhesion of the resist layer when the substrate has a metallic surface or, in particular, surface of tantalum.